Hot-spot detector for heat exchanger

ABSTRACT

A &#39;&#39;&#39;&#39;hot-spot&#39;&#39;&#39;&#39; detecting arrangement for a heat exchanger that receives a flow of hot exhaust gases containing unburned products of combustion. The arrangement detects &#39;&#39;&#39;&#39;hot-spots&#39;&#39;&#39;&#39; or developing fires in deposits of said unburned products of combustion before high temperature is allowed to damage the integrity of the heat exchanger.

United States Patent 91 Wixson et a1.

[ HOT-SPOT DETECTOR FOR HEAT EXCHANGER [75] Inventors: Donald F. Wixson, Wellsville; George K. Ostrander, Angelica,

both of NY.

[73] Assignee: The Air Preheater Company, Inc.,

WeIlsville, NY.

[22] Filed: Mar. 2, 1972 211 App]. No.: 231,273

[52] US. Cl. ..l65/5, 250/83, 165/11, 165/95 [51] Int. Cl. ..F28d 17/00, F28d 19/00 [58] Field of Search ..l65/4, 5,7, 11, 165/95 [56] References Cited UNITED STATES PATENTS 3,183,961 5/1965 Brandt ..165/5 X 3,467,175 9/1969 O'Connor ..165/1 1 [451 May 1, 1973 FOREIGN PATENTS OR APPLICATIONS 9/1968 GreatBritain... ..165/5 7/1962 U.S.S.R. ..165/5 Primary Examiner-AIbert W. Davis, Jr. AltomeyWayne H. Lang et a].

[5 7] ABSTRACT A hot-spot detecting arrangement for a heat exchanger that receives a flow of hot exhaust gases containing unburned products of combustion. The arrangement detects hot-spots or developing fires in deposits of said unburned products of combustion be I fore high temperature is allowed to damage the integrity of the heat exchanger.

14 Claims, 4 Drawing Figures BACKGROUND OF THE INVENTION 1. Field of the Invention In regenerative heat exchange apparatus a mass of heat exchange material commonly comprised of packed element plates is positioned in a hot gas passageway to absorb heat from the hot gases flowing therethrough. As the plates become heated in the hot gas they are moved into a spaced passageway, or the fluids themselves are alternated so that the hot plates transmit heat to the cooler air or other gas flowing therethrough.

As the hot exhaust gases are directed through the heat exchanger fly ash and unburned fuel or soot are deposited on the surface of the packed element plates.

These deposits may in a short time build up to a point where air or gas flow through the heat exchanger will be partially blockaded. If the temperature of the heat exchanger reaches approximately 700 F. to 750 F. heat is exothermically generated therein to a point where the deposit will begin to glow and cause a hotspot." If undetected, the hot-spot" will rapidly increase in temperature to approximately l,400 F. where the metal of the matrix will itselfignite causing catastrophic results to the surrounding structure.

2. Description of Prior Art In past devices it was customary to provide heat exchange apparatus with flame detectors that would signal the occurrence of a fire. However, such flame detectors would respond only after a tire had started and after the temperature had already increased to a point where it was accompanied by a potentially disastrous fire. Other heat responsive devices might respond to a temperature rise in the fluid flowing through the heat exchanger, however, such an increase in temperature would be noted and could be corrected only after the fire had already attained disastrous proportions.

SUMMARY OF THE INVENTION This invention therefore relates to a regenerative heat exchanger apparatus or the like having an arrangement by which ignition of'deposits of combustible products collecting on the surfaceof said apparatus may be quickly detected whereby they may be disposed of in accordance with any suitable arrangement for washing or element cleaning.

The chief objective of my invention therefore is to provide a device for a heat exchanger which will signal a potential fire or hot-spot" well in advance of the occurrence ofa damaging fire.

BRIEF DESCRIPTION OF THE DRAWING DESCRIPTION OF THE PREFERRED EMBODIMENT In the drawings a rotary regenerative heat exchanger comprises a cylindrical casing 10 that encloses a rotor comprised of a cylindrical housing 14 having radial partitions that produce a series of compartments therebetween. The rotor is rotated slowly about its axis by any means such as a motor 15 and reduction gearing arrangement of any suitable type. The rotor contains a mass of regenerative heat transfer material in the form of plates 22 arranged in closely lying layers to provide intermediate passageways that are adapted to channel the flow of fluid therethrough. The heat transfer material first absorbs heat from hot gases entering the heat exchanger through a duct 24 from a boiler or other source of heat to be discharged, after passing over the heat transfer material, through an outlet 26 to which an induced draft fan is usually connected. As the rotor turns slowly about its axis the element that has been heated by the hot gas is moved into a stream of fluid to be heated such as cool air entering the heat exchanger through a duct 28 After passing over the heated elements and absorbing heat therefrom, the heated fluid is discharged through a duct 32 and directed to a boiler furnace or other place of use.

During start-up of a boiler furnace or other heat producing apparatus from which the heat exchanger receives a flow of exhaust gas, incomplete combustion in the burners thereof may cause particles of unburned fuel and other unburned products of combustion to become entrained in the gas exhausting and then to in turn become deposited upon the heat absorbent material of the heat exchanger; These deposits may build up and in ashort time blockage of at least partially block the flow of air or other gas over the heat exchange material, At the same time, the temperature of the deposits and the heat exchange material adjacent thereto will increase because it is not subjected to'a flow of cooling air. As temperatures reach 700 F. to 750 F., the process becomes exothermic and heat is generated in the deposit to a point where an active fire occurs in the deposits, and surrounding metal of the heat exchanger will itself burn when the temperature reaches approximately l,400 F.

Testing has shown that fires may start as small hotspots" 40 near the center of the matrix on small collections of deposits that build up where condensation of liquid vapors in the exhaust gases first occur. These hot-spots will build upto approximately 6 inches in diameter and increase in temperature to about 1,400

F. When this temperature is reached the metal of the heat exchanger ignites and rapidly spreads to engulf adjacent heat exchanger structures with the result that the unit is quickly destroyed.

Inasmuch as such deposits first occurwell within the body of a heat exchanger and develop originally as harmless "hot-spots," this invention is directed to ap paratus that will detect the occurrence of such hotspots in the rotor before a fire actually occurs.

In accordance with this invention a detector 36 for infra-red rays is positioned at the side of the duct leading to the heat exchanger bearing the fluid to be heated. A reflector 38 is positioned axially adjacent the end of the heat exchanger and inlateral alignment with the detector 36 in order that infra-red rays emanating at the hot-spot within the body of the heat exchanger are reflected by reflector 38 thereto. The reflector 38 is mounted on a bracket 40 that is in turn carried on a screw-type mechanism 42 that is turned by a motor 44 and reduction gearing arrangement in order that the reflector 38 may be moved radially from the inner to the outer periphery of the rotor. The motor 44 may be of the reversible type, with the necessary controls to reversely move the reflector after it has reached the inner or outer periphery of the rotor.

Thus, as the rotor of the heat exchanger is rotated about its own axis, the reflector is being moved radially across the rotor so that the entire rotor is systematically passed closely adjacent the reflecting means, and the entire rotor is progressively scanned by the reflector. Accordingly, the energy from the hot-spot will radiate axially between the spaced heat absorbent plates to the reflector where it is in turn reflected to the detector. As the signal is received at the detector it may 1 be relayed to an amplifier (not illustrated), further trigger an alarm, open and close dampers for air or water cooling equipment, or even activate certain fire fighting equipment that will at once eliminate the potential fire.

On large sized heat exchange equipment two or more spaced reflectors may be focused upon a single infrared ray detector whereby the heat exchange matrix of the heat exchanger will be more frequently scanned to detect a hot-spot orpotential fire.

As a practical application it has been found that a single parabolic reflector 52 fixedly mounted at the end of the rotor may be adapted to intercept the infra-red rays emanating in any radial section of the heat exchanger. The reflector 52 will reflect the rays to a single point of focus collector 54 at which location will be positioned the detector 36. The entire reflector and detector assembly may be mounted in a single factory assembled. housing 56 having a side 57 that is transparent to the infra-red rays. Well insulated wires 62 extend from the detector 36 to an amplifier (not illustrated) outside the housing of the heat exchanger whereby a hot-spot would again quickly call for corrective measures.

Inasmuch as prevailing temperatures at the detector 36 may be in excess of 200 F., a cooling system including tubes 58 carrying a cooling fluid from any suitable source may be circulated through the housing 56.

In this manner the entire rotor of a rotary regenerative air preheater may be scanned completely during a single revolution of the rotor and a developing hotspot or fire will be quickly detected so that predetermined corrective measures may be employed.

While the device ofthe invention has been defined as being located in the cool air duct leading to the heat exchanger, it should be understood that it could be installed in other ducts not subject tO excessive heat or corrosion. lt will be obvious to those skilled in the art that other modifications and arrangements may be made In said device without departing from the essence of the invention. It is therefore to be understood that the embodiment shown is illustrative only and not restrictive ofthe invention.

We claim:

l. A heat exchanger having a housing including inlet and outlet ports that permit the independent flow therethrough of a hot and a cool fluid, amatrix in said housing, means for contacting the matrix with the hot and cooler fluids, and a detector responsive to a varia-- tion of infra-red rays in said heat exchanger viewing the matrix of said heat exchanger to detect a variation in the infra-red rays emitted thereby.

2. Heat exchange apparatus as defined in claim 1 having a reflector spaced from an end of said matrix to receive said infra-red rays emitted thereby and reflect them to the detector.

3. Heat exchange apparatus as defined in claim 1 wherein the reflector is a plane mirror, and means moving the plane reflector across the matrix to reflect rays from the matrix to the detector.

4. Heat exchange apparatus as defined in claim 1 wherein the detector responsive to infra-red rays in the matrix is positioned at a side of said housing independent from the hot and cool fluids.

5. Heat exchange apparatus as defined in claim 1 including a parabolic reflector axially spaced from the matrix of the heat exchanger and positioned to view a cross section of said apparatus.

6. Heat exchange apparatus as defined in claim 5 wherein said detector is positioned at the focal point of said parabolic reflector.

7. Regenerative heat exchange apparatus having a cylindrical housing with spaced inlet and outlet ducts that permit the simultaneous flow therethrough of a heating fluid and a fluid to be heated,'a mass of heat absorbent material contained in said housing and adapted to be alternately contacted by the heating fluid and the fluid to be heated, a detector for infra-red rays, a reflector viewing the heat exchanger to reflect rays from the heat absorbent material to the detector, and means for moving said reflector and the heat absorbent material carried in the housing relative to one another to periodically reflect the infra-red rays emitted by the heat absorbent material to said detector.

8. Regenerative heat exchanger apparatus as defined in claim 7 including bearing means rotatably mounting the housing containing the heat absorbent material to permit rotation of said housing alternately between the ducts for the heating fluid and the fluid to be heated whereby the rotor is alternately subjected to said fluids.

9. Regenerative heat exchange apparatus as defined in claim 7 wherein the reflector for infra-red rays originating in the heat exchanger is positioned in the inlet duct for the fluid to be heated to preclude matter entrained in said heating fluid from being deposited on said reflector.

10. Regenerative heat exchange apparatus as defined in claim 7 wherein the heat absorbent material in said housing comprises elongate elements positioned substantially parallel to a line extending between inlet and outlet ducts whereby infra-red rays generated within the heat exchange material travel axially unimpeded to the reflector.

ll. Regenerative heat exchange apparatus having a cylindrical housing with spaced inlet and outlet ducts that permit the simultaneous flow therethrough of a heating fluid and a fluid to be heated, a mass of heat absorbent material carried by said housing, means for subjecting said material alternately to the heating fluid and the fluid to be heated, a detector housing mounted in a fluid duct adjacent the mass of heat absorbent material, a reflector in said housing directed toward said heat absorbent material, and an infra-red detector positioned in the detector housing to receive rays reflected thereto by the reflector in the housing.

12. Regenerative heat exchange apparatus as defined in claim 11 wherein the reflector in said detector housing is shaped as a parabola.

l3. Regenerative heat exchange apparatus as definedin claim 12 wherein said detector housing is positioned 

1. A heat exchanger having a housing including inlet and outlet ports that permit the independent flow therethrough of a hot and a cool fluid, a matrix in said housing, means for contacting the matrix with the hot and cooler fluids, and a detector responsive to a variation of infra-red rays in said heat exchanger viewing the matrix of said heat exchanger to detect a variation in the infra-red rays emitted thereby.
 2. Heat exchange apparatus as defined in claim 1 having a reflector spaced from an end of said matrix to receive said infra-red rays emitted thereby and reflect them to the detector.
 3. Heat exchange apparatus as defined in claim 1 wherein the reflector is a plane mirror, and means moving the plane reflector across the matrix to reflect rays from the matrix to the detector.
 4. Heat exchange apparatus as defined in claim 1 wherein the detector responsive to infra-red rays in the matrix is positioned at a side of said housing independent from the hot and cool fluids.
 5. Heat exchange apparatus as defined in claim 1 including a parabolic reflector axially spaced from the matrix of the heat exchanger and positioned to view a cross section of said apparatus.
 6. Heat exchange apparatus as defined in claim 5 wherein said detector is positioned at the focal point of said parabolic reflector.
 7. Regenerative heat exchange apparatus having a cylindrical housing with spaced inlet and outLet ducts that permit the simultaneous flow therethrough of a heating fluid and a fluid to be heated, a mass of heat absorbent material contained in said housing and adapted to be alternately contacted by the heating fluid and the fluid to be heated, a detector for infra-red rays, a reflector viewing the heat exchanger to reflect rays from the heat absorbent material to the detector, and means for moving said reflector and the heat absorbent material carried in the housing relative to one another to periodically reflect the infra-red rays emitted by the heat absorbent material to said detector.
 8. Regenerative heat exchanger apparatus as defined in claim 7 including bearing means rotatably mounting the housing containing the heat absorbent material to permit rotation of said housing alternately between the ducts for the heating fluid and the fluid to be heated whereby the rotor is alternately subjected to said fluids.
 9. Regenerative heat exchange apparatus as defined in claim 7 wherein the reflector for infra-red rays originating in the heat exchanger is positioned in the inlet duct for the fluid to be heated to preclude matter entrained in said heating fluid from being deposited on said reflector.
 10. Regenerative heat exchange apparatus as defined in claim 7 wherein the heat absorbent material in said housing comprises elongate elements positioned substantially parallel to a line extending between inlet and outlet ducts whereby infra-red rays generated within the heat exchange material travel axially unimpeded to the reflector.
 11. Regenerative heat exchange apparatus having a cylindrical housing with spaced inlet and outlet ducts that permit the simultaneous flow therethrough of a heating fluid and a fluid to be heated, a mass of heat absorbent material carried by said housing, means for subjecting said material alternately to the heating fluid and the fluid to be heated, a detector housing mounted in a fluid duct adjacent the mass of heat absorbent material, a reflector in said housing directed toward said heat absorbent material, and an infra-red detector positioned in the detector housing to receive rays reflected thereto by the reflector in the housing.
 12. Regenerative heat exchange apparatus as defined in claim 11 wherein the reflector in said detector housing is shaped as a parabola.
 13. Regenerative heat exchange apparatus as defined in claim 12 wherein said detector housing is positioned in the inlet duct for the fluid to be heated.
 14. Regenerative heat exchange apparatus as defined in claim 13 including conduits in said detector housing that direct a cooling fluid therethrough to effectively lower the temperature thereof to a temperature substantially less than that of the fluid in the duct in which the detector housing is positioned. 